The invention concerns refining and conversion of heavy liquid hydrocarbon fractions containing inter alia asphaltenes and sulphur and metallic impurities, such as atmospheric residues, vacuum residues, deasphalted oils, pitches, asphalts mixed with an aromatic distillate, coal hydrogenates or heavy oils from any source and particularly from asphaltic sands or oil shales.
These charges which can be treated according to the invention generally contain at least 100 ppm by weight of metals (nickel and/or vanadium), at least 1% by weight of sulphur and at least 2% by weight of asphaltenes.
The object of the catalytic hydrotreatment of these charges is both to refine, i.e. substantially reduce, their content of asphaltenes, metals, sulphur and other impurities, while at the same time improving the hydrogen to carbon ratio (H/C) and converting them more or less partially to lighter cuts. The various effluents thus obtained can act as bases for the production of high quality fuel, gas oil and petrol, or charges for other units such as residue cracking.
The problem posed by the catalytic hydrotreatment of these charges stems from the fact that the impurities are deposited bit by bit on the catalyst in the form of metals and coke, and tend to deactivate and rapidly clog the catalytic system, necessitating a stoppage for its replacement.
Methods of hydrotreatment for this type of charge must therefore be designed to allow the longest possible operating cycle without stopping the unit. The objective is to achieve a one year operating cycle at the minimum, or a minimum of eleven months' continuous operation plus a maximum of one month's stoppage to replace the whole catalytic system.